Electron paramagnetic resonance (EPR) measurements were performed on GaN:Mg epitaxial films grown on sapphire by chemical vapor deposition. Isochronal annealing studies between 200 and 850°C show that the temperature dependence for activation of a resonance at g∥=2.1 was consistent with the previous interpretation of the signal as a Mg-related acceptor. Furthermore, EPR measurements performed on samples after consecutive 30-min-heat treatments in dry N2, N2:H2, and dry N2 showed that the center could be activated, passivated, and reactivated as expected for the p-type acceptor center in GaN.
